US20010045365A1 - Molten salt electrolysis of alkali metals - Google Patents
Molten salt electrolysis of alkali metals Download PDFInfo
- Publication number
- US20010045365A1 US20010045365A1 US09/861,054 US86105401A US2001045365A1 US 20010045365 A1 US20010045365 A1 US 20010045365A1 US 86105401 A US86105401 A US 86105401A US 2001045365 A1 US2001045365 A1 US 2001045365A1
- Authority
- US
- United States
- Prior art keywords
- sodium
- cell
- electrolyte
- alkali metal
- strontium
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Granted
Links
- 238000005868 electrolysis reaction Methods 0.000 title claims abstract description 11
- 229910052783 alkali metal Inorganic materials 0.000 title description 14
- 150000001340 alkali metals Chemical class 0.000 title description 14
- 150000003839 salts Chemical class 0.000 title description 7
- 238000000034 method Methods 0.000 claims abstract description 37
- 230000008569 process Effects 0.000 claims abstract description 36
- 239000003792 electrolyte Substances 0.000 claims abstract description 24
- 229910052712 strontium Inorganic materials 0.000 claims abstract description 14
- 229910001508 alkali metal halide Inorganic materials 0.000 claims abstract description 9
- 150000008045 alkali metal halides Chemical class 0.000 claims abstract description 9
- -1 strontium halide Chemical class 0.000 claims abstract description 9
- FAPWRFPIFSIZLT-UHFFFAOYSA-M Sodium chloride Chemical group [Na+].[Cl-] FAPWRFPIFSIZLT-UHFFFAOYSA-M 0.000 claims description 34
- 239000011780 sodium chloride Substances 0.000 claims description 17
- 229910001631 strontium chloride Inorganic materials 0.000 claims description 10
- AHBGXTDRMVNFER-UHFFFAOYSA-L strontium dichloride Chemical group [Cl-].[Cl-].[Sr+2] AHBGXTDRMVNFER-UHFFFAOYSA-L 0.000 claims description 10
- DGAQECJNVWCQMB-PUAWFVPOSA-M Ilexoside XXIX Chemical compound C[C@@H]1CC[C@@]2(CC[C@@]3(C(=CC[C@H]4[C@]3(CC[C@@H]5[C@@]4(CC[C@@H](C5(C)C)OS(=O)(=O)[O-])C)C)[C@@H]2[C@]1(C)O)C)C(=O)O[C@H]6[C@@H]([C@H]([C@@H]([C@H](O6)CO)O)O)O.[Na+] DGAQECJNVWCQMB-PUAWFVPOSA-M 0.000 description 28
- 229910052708 sodium Inorganic materials 0.000 description 28
- 239000011734 sodium Substances 0.000 description 28
- 239000011575 calcium Substances 0.000 description 12
- OYPRJOBELJOOCE-UHFFFAOYSA-N Calcium Chemical compound [Ca] OYPRJOBELJOOCE-UHFFFAOYSA-N 0.000 description 11
- 229910052791 calcium Inorganic materials 0.000 description 11
- 229910001626 barium chloride Inorganic materials 0.000 description 7
- WDIHJSXYQDMJHN-UHFFFAOYSA-L barium chloride Chemical compound [Cl-].[Cl-].[Ba+2] WDIHJSXYQDMJHN-UHFFFAOYSA-L 0.000 description 7
- KEAYESYHFKHZAL-UHFFFAOYSA-N Sodium Chemical compound [Na] KEAYESYHFKHZAL-UHFFFAOYSA-N 0.000 description 6
- UXVMQQNJUSDDNG-UHFFFAOYSA-L Calcium chloride Chemical compound [Cl-].[Cl-].[Ca+2] UXVMQQNJUSDDNG-UHFFFAOYSA-L 0.000 description 5
- 229910000831 Steel Inorganic materials 0.000 description 5
- 239000001110 calcium chloride Substances 0.000 description 5
- 229910001628 calcium chloride Inorganic materials 0.000 description 5
- 238000004519 manufacturing process Methods 0.000 description 5
- 239000010959 steel Substances 0.000 description 5
- CIOAGBVUUVVLOB-UHFFFAOYSA-N strontium atom Chemical compound [Sr] CIOAGBVUUVVLOB-UHFFFAOYSA-N 0.000 description 5
- 239000000126 substance Substances 0.000 description 5
- 229910052788 barium Inorganic materials 0.000 description 4
- DSAJWYNOEDNPEQ-UHFFFAOYSA-N barium atom Chemical compound [Ba] DSAJWYNOEDNPEQ-UHFFFAOYSA-N 0.000 description 4
- 229910052736 halogen Inorganic materials 0.000 description 4
- 150000002367 halogens Chemical class 0.000 description 4
- 238000002844 melting Methods 0.000 description 4
- 230000008018 melting Effects 0.000 description 4
- 239000000203 mixture Substances 0.000 description 4
- WHXSMMKQMYFTQS-UHFFFAOYSA-N Lithium Chemical compound [Li] WHXSMMKQMYFTQS-UHFFFAOYSA-N 0.000 description 3
- 230000008859 change Effects 0.000 description 3
- 238000001914 filtration Methods 0.000 description 3
- 229910052744 lithium Inorganic materials 0.000 description 3
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 description 2
- ZLMJMSJWJFRBEC-UHFFFAOYSA-N Potassium Chemical compound [K] ZLMJMSJWJFRBEC-UHFFFAOYSA-N 0.000 description 2
- 230000015572 biosynthetic process Effects 0.000 description 2
- 229910052792 caesium Inorganic materials 0.000 description 2
- TVFDJXOCXUVLDH-UHFFFAOYSA-N caesium atom Chemical compound [Cs] TVFDJXOCXUVLDH-UHFFFAOYSA-N 0.000 description 2
- 230000008030 elimination Effects 0.000 description 2
- 238000003379 elimination reaction Methods 0.000 description 2
- 229910052730 francium Inorganic materials 0.000 description 2
- KLMCZVJOEAUDNE-UHFFFAOYSA-N francium atom Chemical compound [Fr] KLMCZVJOEAUDNE-UHFFFAOYSA-N 0.000 description 2
- 229910002804 graphite Inorganic materials 0.000 description 2
- 239000010439 graphite Substances 0.000 description 2
- 230000004048 modification Effects 0.000 description 2
- 238000012986 modification Methods 0.000 description 2
- 229910052700 potassium Inorganic materials 0.000 description 2
- 239000011591 potassium Substances 0.000 description 2
- 238000000746 purification Methods 0.000 description 2
- 229910052701 rubidium Inorganic materials 0.000 description 2
- IGLNJRXAVVLDKE-UHFFFAOYSA-N rubidium atom Chemical compound [Rb] IGLNJRXAVVLDKE-UHFFFAOYSA-N 0.000 description 2
- PUZPDOWCWNUUKD-UHFFFAOYSA-M sodium fluoride Chemical compound [F-].[Na+] PUZPDOWCWNUUKD-UHFFFAOYSA-M 0.000 description 2
- ZAMOUSCENKQFHK-UHFFFAOYSA-N Chlorine atom Chemical compound [Cl] ZAMOUSCENKQFHK-UHFFFAOYSA-N 0.000 description 1
- 238000004458 analytical method Methods 0.000 description 1
- 230000008901 benefit Effects 0.000 description 1
- 239000011449 brick Substances 0.000 description 1
- 238000006243 chemical reaction Methods 0.000 description 1
- 150000003841 chloride salts Chemical class 0.000 description 1
- 239000000460 chlorine Substances 0.000 description 1
- 229910052801 chlorine Inorganic materials 0.000 description 1
- 150000001875 compounds Chemical class 0.000 description 1
- 238000001816 cooling Methods 0.000 description 1
- 238000000354 decomposition reaction Methods 0.000 description 1
- 238000004945 emulsification Methods 0.000 description 1
- 238000005516 engineering process Methods 0.000 description 1
- 239000012535 impurity Substances 0.000 description 1
- 229910052751 metal Inorganic materials 0.000 description 1
- 239000002184 metal Substances 0.000 description 1
- 238000002156 mixing Methods 0.000 description 1
- 238000001556 precipitation Methods 0.000 description 1
- 230000009257 reactivity Effects 0.000 description 1
- 230000009467 reduction Effects 0.000 description 1
- 230000000717 retained effect Effects 0.000 description 1
- 239000011833 salt mixture Substances 0.000 description 1
Classifications
-
- C—CHEMISTRY; METALLURGY
- C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
- C25C—PROCESSES FOR THE ELECTROLYTIC PRODUCTION, RECOVERY OR REFINING OF METALS; APPARATUS THEREFOR
- C25C3/00—Electrolytic production, recovery or refining of metals by electrolysis of melts
- C25C3/02—Electrolytic production, recovery or refining of metals by electrolysis of melts of alkali or alkaline earth metals
Definitions
- a hydraulically permeable diaphragm such as a steel mesh screen, is used to separate the cathode and anode compartments.
Landscapes
- Chemical & Material Sciences (AREA)
- Engineering & Computer Science (AREA)
- Chemical Kinetics & Catalysis (AREA)
- Electrochemistry (AREA)
- Materials Engineering (AREA)
- Metallurgy (AREA)
- Organic Chemistry (AREA)
- Electrolytic Production Of Metals (AREA)
Abstract
An electrolysis process is provided which comprises carrying out the process in an electrolyte that comprises an alkali metal halide and a strontium halide. The process can be carried out at a current density in the range of from about 7 to about 10 kA/m2.
Description
- This invention relates to a molten salt electrolysis process for producing an alkali metal using a binary alkali metal halide and strontium halide molten salt electrolyte.
- The alkali metals, sodium, potassium, lithium, rubidium, cesium and francium are not found in elemental form in nature because of their high reactivity which causes them to combine with other elements to form various compounds. Electrolytic reduction is necessary to produce an alkali metal in its elemental form. The currently used process, on a world-wide basis, is the so-called “DOWNS PROCESS”, which was introduced in the early part of the 20 th century for the production of sodium and lithium from their chlorides (Marshall Sittig, Sodium, Its Manufacture, Properties and Uses, American Chemical Society Monograph Series, Reinhold Published Corp., New York; Chapman & Hall, Ltd., London (1956) and Kirk-Othmer Encyclopedia of Chemical Technology, 4th Edition, Wiley/Interscience, New York (1997), Vol. 22, p. 327 to 354). The Downs Process uses a molten salt electrolyte consisting of a mixture of NaCl, CaCl2, and BaCl2 in order to reduce the melting temperature of the electrolyte to less than 600° C. This makes the process more practical compared to using pure NaCl which has a much higher melting point of about 800° C. The most important of the alkali metals, for industrial uses, is sodium. Sodium metal produced by the conventional Downs Process contains small amounts of calcium metal, which is co-deposited with the sodium at the cathode during electrolysis because the decomposition potential of calcium is close to that of sodium. Fairly elaborate and costly cooling/precipitation/filtration procedures are necessary to remove the calcium from the sodium metal produced by the conventional Downs Process. These purification steps remove practically all of the barium and most of the calcium. However, a significant amount of calcium is retained in the commercially produced sodium even after the purification process. Typical commercial sodium metal contains about 200 to 400 parts per million by weight (ppm) of calcium. For some applications (particularly nuclear, but also some chemical and electronic uses), an essentially calcium-free sodium is required. There are chemical routes to further purify sodium metal but these routes are extremely expensive.
- Electrolytes which eliminated calcium and, therefore, produced calcium-free sodium were developed some years ago. These electrolytes are based on ternary and quaternary compositions containing NaCl, SrCl 2, BaCl2 (ternary) and/or NaCl, SrCl2, BaCl2, NaF (quaternary) in near-eutectic proportions having melting temperatures of about 550 to 560° C. (U.S. Pat. No. 2,850,442). A binary NaCl/SrCl2, electrolyte was also developed for the elimination of calcium from the sodium metal product (U.S. Pat. No. 3,119,765).
- These electrolytes can be used in the standard Downs-type electrolytic cells without significant cell modification and/or change in operating conditions (same electrolyte/cell operating temperature of about 600° C. and same cell voltage of about 7.0 to 7.5 V) because the melting temperature of these compositions is about the same as that for the standard NaCl/CaCl 2,BaCl2 electrolyte. Current efficiency of cells operated with the ternary strontium electrolyte “bath” are in the range of 85% to 89%, similar to the standard NaCl/CaCl2,/BaCl2 bath. The quaternary bath can give somewhat higher current efficiencies but has the disadvantage that it attacks the brick lining of the electrolytic cells. Sodium made with the strontium-containing electrolytes is near calcium-free, but contains about 1000 ppm strontium and barium, which can be removed to low levels by a simpler conventional filtration process.
- In the above electrolyte systems, cell operating temperatures are typically about 600° C. when operating at high current densities in the order of 5 to 6 kA/m 2. Current efficiency is reduced at higher temperatures, for example when operating at current densities higher than 5 to 6 kA/m2, due to formation of “sodium fog” (emulsification of sodium in the electrolyte). This causes sodium losses and, therefore, losses in current efficiency when operating at higher current densities and temperatures above about 600° C. in a Downs Process with the standard NaCl/CaCl2,/BaCl2 electrolyte. When in the form of sodium fog, sodium can partially migrate to the anode where the sodium is re-oxidized or reacts with chlorine to form NaCl. Sodium fog can also migrate to the surface of the molten electrolyte, which is exposed to air, whereupon sodium can also become re-oxidized.
- Therefore, it is highly desirable to develop a process that is capable of operating at high current densities while producing substantially calcium-free sodium without a large increase in operating costs. An advantage of the present invention is the substantial elimination of calcium in the alkali metal product and increased electrolysis cell output without the need for substantial change in the cell design.
- The present invention provides a molten salt electrolysis process for producing an alkali metal comprising carrying out the process using a binary electrolyte comprising an alkali metal halide and strontium halide, wherein the process is carried out at a high current density.
- The present invention provides a process for producing an alkali metal by electrolysis from a binary molten salt electrolyte comprising an alkali metal halide and a strontium halide. In particular, the process is carried out at a high current density. The term “high current density” refers to about 7 to about 10, preferably about 7 to about 8, kA/m 2. Current density is defined as the current in Amperes per unit area of effective electrode surface area. Increasing the current density on a given cell design can be carried out by increasing the current through the cell. For a cell of given design the electrode area is constant and an increase in current density means an increase in total current and, therefore, a corresponding increase in sodium production per unit time (provided there is no change in current efficiency).
- The process of the invention can be carried out at any suitable temperature that can achieve an increase in sodium production per unit time. Generally, the temperature can be in the range of from about 605 to about 625° C.
- Any alkali metal halides can be used in the invention. The term “alkali metal” refers to lithium, sodium, potassium, rubidium, cesium, francium, or combinations of two or more thereof. The presently preferred alkali metal halide is sodium chloride for it is widely used in electrolysis and sodium produced therefrom is commercially important. Similarly, strontium chloride is the preferred strontium halide.
- The weight ratio of alkali metal halide to strontium halide can be any ratio so long as the ratio can produce a high purity alkali metal having calcium levels of less than about 50 ppm, barium levels of less than about 30 ppm, and strontium levels of less than about 600 ppm, preferably calcium levels of less than about 20 ppm, barium levels of less than about 10 ppm, and strontium levels of less than about 300 ppm. Generally, the ratio can be in the range of from about 35 NaCl/65 SrCl 2 to about 19 NaCl/81SrCl2. For example, a binary electrolyte composition can contain 27 weight % NaCl and about 73 weight % SrCl2. Impurities in the electrolyte are preferably kept to less than about 2% by weight.
- The process of the present invention for molten salt electrolysis of alkali metals uses a Downs cell design to carry out the process, originally disclosed in U.S. Pat. No. 1,501,756. A detailed description of this cell is given in Ullmann's Encyclopedia of Industrial Chemistry, 5 th Ed., Vol. A24, VCH Verlagsgesellschaft, Germany, pp. 284-288 (1993). The pertinent portions of these documents are hereby incorporated into this specification by this reference thereto.
- The ensuing discussion provides an example of a Downs cell useful in the present invention. However, it should be recognized that other designs based on a Downs cell can also be useful. The Downs cell will typically have a cylindrical brick-lined, steel casing. Cylindrical graphite anodes project upward through the bottom of the steel casing. Cylindrical steel cathodes project upward surrounding the anodes. In operation, the alkali metal is deposited on the inside surface of the steel cathodes and halogen gas is liberated at the graphite anodes. Typically, in a cell with four electrodes, the halogen is collected from the anodes into a gas dome from which the halogen exits the cell. The alkali metal rises in the electrolyte from the cathodes and is collected in a single compartment “collector ring” covering all four cathodes.
- To prevent back-mixing and reaction of the alkali metal and halogen, a hydraulically permeable diaphragm, such as a steel mesh screen, is used to separate the cathode and anode compartments.
- The following example is provided to further illustrate the invention and are not to be construed to unduly limit the scope of the invention.
- This example shows that the process of the invention produces more sodium per cell than a process using the conventional process.
- A conventional Downs electrolysis cell for sodium production was used. A dry salt mixture of 27 wt % NaCl and 73 wt % SrCl 2 was melted in the Downs cell and electrolyzed for 11 days, without any sign of sodium fog formation, at a cell voltage of 6.8 to 7.2 V, at a cell temperature of 610 to 615° C. and using a very high current density of about 7.5 kA/m2 corresponding to a total cell current of 55,000 A. Cell output of sodium metal was about 2100 lbs (954.5 kg) per day which is about 20% to 25% higher than for the same type of Downs cell using conventional NaCl/CaCl2/BaCl2 electrolyte and using 45,000 A total current corresponding to about 6 kA/m2 current density. Sodium made with the NaCl/SrCl2 electrolyte was found to be of very high purity. After the usual sodium filtration step the chemical analysis showed less than 20 ppm Ca, less than 10 ppm Ba and less than 300 ppm of Sr.
- The present invention is, of course, in no way restricted to the specific disclosure of the specification and drawing, but also encompasses any modifications within the scope of the appended claims.
Claims (8)
1. An electrolysis process comprising carrying out said process at a current density in the range of from about 7 to about 10 kA/m2 and in an electrolyte comprising an alkali metal halide and a strontium halide.
2. A process according to , wherein said alkali metal halide is sodium chloride.
claim 1
3. A process according to , wherein said strontium halide is strontium chloride.
claim 1
4. A process according to , wherein said strontium halide is strontium chloride.
claim 2
5. A process according to , wherein said process is carried out at a current density in the range of from about 7 to about 8 kA/m2.
claim 1
6. A process according to , wherein said process is carried out at a current density in the range of from about 7 to about 8 kA/m2.
claim 2
7. A process according to , wherein said process is carried out at a current density in the range of from about 7 to about 8 kA/m2.
claim 3
8. A process according to , wherein said process is carried out at a current density in the range of from about 7 to about 8 kA/m2.
claim 4
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US09/861,054 US6669836B2 (en) | 2000-05-19 | 2001-05-18 | Molten salt electrolysis of alkali metals |
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US20575500P | 2000-05-19 | 2000-05-19 | |
| US09/861,054 US6669836B2 (en) | 2000-05-19 | 2001-05-18 | Molten salt electrolysis of alkali metals |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| US20010045365A1 true US20010045365A1 (en) | 2001-11-29 |
| US6669836B2 US6669836B2 (en) | 2003-12-30 |
Family
ID=26900740
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| US09/861,054 Expired - Fee Related US6669836B2 (en) | 2000-05-19 | 2001-05-18 | Molten salt electrolysis of alkali metals |
Country Status (1)
| Country | Link |
|---|---|
| US (1) | US6669836B2 (en) |
Families Citing this family (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US7713400B2 (en) * | 2006-12-13 | 2010-05-11 | Mcwhorter Edward Milton | Method of making a nodular electrolytic flocculant |
Family Cites Families (6)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US1501756A (en) | 1922-08-18 | 1924-07-15 | Roessler & Hasslacher Chemical | Electrolytic process and cell |
| US2850442A (en) | 1956-04-11 | 1958-09-02 | Du Pont | Bath for the manufacture of sodium |
| US3119756A (en) | 1962-10-22 | 1964-01-28 | Ethyl Corp | Production of sodium |
| US4187155A (en) * | 1977-03-07 | 1980-02-05 | Diamond Shamrock Technologies S.A. | Molten salt electrolysis |
| US5015343A (en) * | 1987-12-28 | 1991-05-14 | Aluminum Company Of America | Electrolytic cell and process for metal reduction |
| US5118396A (en) * | 1989-06-09 | 1992-06-02 | The Dow Chemical Company | Electrolytic process for producing neodymium metal or neodymium metal alloys |
-
2001
- 2001-05-18 US US09/861,054 patent/US6669836B2/en not_active Expired - Fee Related
Also Published As
| Publication number | Publication date |
|---|---|
| US6669836B2 (en) | 2003-12-30 |
Similar Documents
| Publication | Publication Date | Title |
|---|---|---|
| US5024737A (en) | Process for producing a reactive metal-magnesium alloy | |
| CN1070243C (en) | Electrolytic production process for magnesium and its alloys | |
| KR102004920B1 (en) | Metal refining method by using liquid metal cathode | |
| US4563339A (en) | Process for the preparation of magnesium chloride for use as an electrolyte in electrolytic production of magnesium metal | |
| US4988417A (en) | Production of lithium by direct electrolysis of lithium carbonate | |
| US2722509A (en) | Production of titanium | |
| US4780186A (en) | Lithium transport cell process | |
| US3725222A (en) | Production of aluminum | |
| US6676824B2 (en) | Process for purification of molten salt electrolytes | |
| US3226311A (en) | Process of producing calcium by electrolysis | |
| US6669836B2 (en) | Molten salt electrolysis of alkali metals | |
| US2850442A (en) | Bath for the manufacture of sodium | |
| US2707170A (en) | Electrodeposition of titanium | |
| US5853560A (en) | Electrolytic magnesium production process using mixed chloride-fluoride electrolytes | |
| US2798844A (en) | Electrolyte for titanium production | |
| US4464234A (en) | Production of aluminum metal by electrolysis of aluminum sulfide | |
| US3344049A (en) | Method of producing lithium | |
| US4802970A (en) | Process for preparing fluorine by electrolysis of calcium fluoride | |
| US2880151A (en) | Electrolytic production of magnesium metal | |
| US2813069A (en) | Porous anode | |
| US4595466A (en) | Metal electrolysis using a low temperature bath | |
| US2876180A (en) | Fused salt bath for the electrodeposition of transition metals | |
| US3020221A (en) | Process for producing sodium | |
| US3558452A (en) | Electrolysis cell current efficiency with solid oxidizing agents | |
| US3558451A (en) | Electrolysis cell current efficiency |
Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| AS | Assignment |
Owner name: NEW MEXICO TECHNICAL RESEARCH FOUNDATION, NEW MEXI Free format text: ASSIGNMENT OF ASSIGNORS INTEREST;ASSIGNORS:KEPPLER, STEPHEN JOHN;MESSING, THOMAS A.;PROULX, KEVIN BERNARD;AND OTHERS;REEL/FRAME:011830/0637 Effective date: 20010516 |
|
| FEPP | Fee payment procedure |
Free format text: PAT HOLDER CLAIMS SMALL ENTITY STATUS, ENTITY STATUS SET TO SMALL (ORIGINAL EVENT CODE: LTOS); ENTITY STATUS OF PATENT OWNER: SMALL ENTITY |
|
| FPAY | Fee payment |
Year of fee payment: 4 |
|
| REMI | Maintenance fee reminder mailed | ||
| LAPS | Lapse for failure to pay maintenance fees | ||
| STCH | Information on status: patent discontinuation |
Free format text: PATENT EXPIRED DUE TO NONPAYMENT OF MAINTENANCE FEES UNDER 37 CFR 1.362 |
|
| FP | Lapsed due to failure to pay maintenance fee |
Effective date: 20111230 |